This is a new application under PAS-10-098, Technology-based Adherence Interventions for Substance Abusing Populations with HIV (R34). New methods to promote HIV treatment adherence are needed for drug users, ethnic minorities, and women, who reside outside major metropolitan areas who have worse health outcomes. Familiar technological devices such as mobile phones could overcome some of the health disparities seen among rural HIV+ patients. In this project, investigators will develop and test the feasibility and promise of a text messaging system that uses Ecological Momentary Assessment (EMA) methods to detect nonadherence and drug use episodes, then immediately intervenes to improve HIV treatment adherence (both medication adherence and treatment engagement) in drug users living with HIV/AIDS. Using formative research with the targeted patients and partnership with a technology developer, we will develop the application and administrative system, Treatment Extension by Text (Text). Text will assess routine adherence, allow users to report critical events, and respond to randomly timed queries about adherence, drug use, and drug craving. When the Text EMA application detects threats to adherence, it will deliver a personalized, tailored intervention text message chosen by the participant. These customized messages will remind the user to take medications on time and reduce drug use. Investigators will pilot test the new adherence tool against treatment as usual over a three month period in a small pilot randomized trial to determine the feasibility, acceptability, and promise of Text. This R34 is a Stage 1b/2a project in the Stage Model of Behavioral Therapy Development in that it will develop novel interventions and methods, and generate preliminary estimates of effect sizes that will determine whether a larger, more expensive clinical trial with a longer follow-up period and evaluation of cost-effectiveness is warranted. By using technology to assess and detect episodes of nonadherence, drug use, and drug craving in real time, the project will deliver an intervention "on the fly" in time to help the person resume medication adherence before health damages occur. If successful, Text has the possibility of rapid scale-up for further trials across the rural U.S. to follow. PUBLIC HEALTH RELEVANCE: This project will develop and pilot test a text messaging system for mobile phones to assess HIV treatment adherence, quickly detect problems as they occur, and send personalized intervention messages to help rural and non-urban drug using patients achieve HIV medication adherence and interrupt drug use. This intervention could be scaled up quickly as a novel, sustainable approach to maintaining treatment adherence. Lessons learned could hasten the development of interventions for other chronic diseases in the U.S.